Periodic Table and Atomic Structure (LC 2026) (Leaving Cert Chemistry): Revision Notes

1.2 - Redox Reactions of Group VII Elements and Displacement Reactions of Metals

Experiment Summary

This experiment investigates two main chemical processes:

(a) Redox reactions of Group VII elements (halogens) – reactions between chlorine, bromine, and iodine with their halide salts.

(b) Displacement reactions of metals – how magnesium and zinc displace copper from copper(II) sulphate, demonstrating the reactivity of metals based on the electrochemical series.

Materials and Apparatus Required

Chemicals

• For Redox Reactions of Halogens:
  • Chlorine solution
  • Bromine solution
  • Iodine solution
  • Sodium chloride solution
  • Sodium bromide solution
  • Potassium iodide solution
  • Iron(II) sulphate solution
  • Sodium sulfite solution
• For Displacement Reactions:
  • Acidified copper(II) sulphate solution
  • Zinc powder
  • Magnesium ribbon

Apparatus

• Safety glasses
• PVC gloves
• Pasteur pipettes
• Test tubes and rack
• Boiling tubes
• Sandpaper (to clean magnesium ribbon)
• Fume cupboard (for handling chlorine and bromine)
• Bunsen burner

Safety Precautions

• Wear safety glasses at all times.
• Chlorine and bromine are poisonous. Work in a fume cupboard to avoid inhalation.
• Iodine can irritate the skin; handle it with care.
• Concentrated hydrochloric acid and sulfuric acid are corrosive to the skin and eyes.
• Sodium hydroxide is caustic and harmful to the skin and eyes.
• Silver nitrate is hazardous to the eyes and will stain the skin.
• Dispose of all chemical waste responsibly by neutralising it with water and proper dilution.

Method

Redox Reactions of Halogens:

1. In separate test tubes, mix:

• Chlorine with bromide and iodide ions.
• Bromine with iodide ions.

2. Observe and record the colour changes.
3. Test reactions of halogens with iron(II) sulfate and sodium sulfite.

• Chlorine will oxidise $Fe²⁺$to $Fe³⁺$, and oxidise $SO₃²⁻$to $SO₄²⁻$

Displacement Reactions of Metals:

1. Half-fill two boiling tubes with acidified copper(II) sulphate solution.
2. Add magnesium ribbon to one tube and zinc powder to the other.
3. Observe the reactions and note any colour changes and gas evolution.

Results

Redox Reactions of Halogens:

• Chlorine oxidises bromide ions to form $Br₂$ (orange) and iodide ions to form $I₂$ (brown).
• Bromine oxidises iodide ions to $I₂$.

Displacement Reactions of Metals:

• Both magnesium and zinc displace copper, producing a brown precipitate of copper and a colourless solution of magnesium or zinc sulphate.

Example Questions with Answers